Praised for his visionary revitalisation of the national collection but scorned for his perceived love-affair with conceptualism, few in the art world divide opinion like Tate director Sir Nicholas Serota. As he signs a new, permanent contract with the gallery Patrick Kingsley meets the most influential figure in British art.

Nicholas Serota has enemies. You wouldn't know it from his kindly demeanour, his tidy shirtsleeves and from the way he revitalised both the Tate and the Whitechapel Galleries, but someone somewhere has always taken issue with something he's done.

As a member of the Young Tate, he enraged the powers-that-were with his independent outreach projects and unofficial exhibitions. A decade later, as the new Director of the Whitechapel, commentators criticised his year-long closure of the gallery whilst others condemned the avant-garde content of his exhibitions. Many traditionalists resented his eventual appointment as Tate director, still more hated the plans to install Tate Modern inside an old power-station and, of late, the Stuckists - a collection of figuratively-minded artists - have mounted a fierce campaign to remove him office.

Nothing, however, more riled his opponents than his decision to buy several pieces of work from current Tate Artist Trustees. Most notably, his 2005 acquisition of trustee Chris Ofili's The Upper Room sparked a huge controversy. The Charity Commission deemed it illegal; the Daily Telegraph called the debacle "one of the most serious indictments of [a national cultural institution] in living memory"; and the Stuckists implied he was guilty of cronyism. Their leader, Charles Thomson, alleged that "Serota, as the director, chooses the trustees, and the trustees are then responsible for reappointing the director. The director then buys the trustees' work... Basically the Tate are appointing their own bosses."

Serota himself vigorously denies this version of events: "Firstly, I don't choose the trustees. The trustees are appointed by the PM on the recommendation of a panel of [other] Tate trustees together with an independent assessor. I don't have any part to play in their appointment." Moreover, he argues, it isn't as if these Trustees had anything to gain by selling to the Tate. "Why would I want to win their support? These are artists who have a place in the world already; people are falling over themselves to buy Chris Ofili's work and Peter Doig's work. The issue is not, ‘Is the Tate is doing this to curry favour with them?' but, actually, ‘Can the Tate get hold of the work?'" Most convincingly, he points out that, in fact, "Chris Ofili sold us The Upper Room at a price way below what he could have achieved elsewhere... Many works by Ofili had sold for higher prices at auction."

Which all sounds perfectly reasonable. Yet the fact remains that the Tate, however well-intentioned, broke charity law not just in Ofili's case but in sixteen other instances too. Who was to blame? Serota is quick to lay responsibility on age-old institutional malpractice: "we had been following a practice which had been running for fifty years." He is keen - almost defensively so - to stress that Tate practice has improved immeasurably, thanks to suggestions by the Charity Commission. "We're a more open organization than any equivalent organization in the world. Can you find the minutes of the trustees' meeting of the Museum of Modern Art on their website, or the Pompidou? You can't. So we're at the forefront of being as open as we possibly can."

There's an inkling that Serota, quite naturally, feels slightly mistreated by the media as a result of the whole affair. "The press took the side of the argument put forward by one group, and didn't really give full weight to the other... You can't have it both ways; on the one hand we're criticised for not having bought Rachel Whiteread's house or Damien Hirst's shark, and then when we do go out and buy a Chris Ofili or a Peter Doig, we're also criticised."

Damien Hirst is himself very much in the news these days. The ex-YBA has just become the first well-established artist to by-pass museums and sell directly to the public through a solo show at an auction house. The success of this individual venture seems to imply two things: firstly, that the power of the major museums is about to be eroded; and secondly that the art world is not being affected by the current financial storms. Serota, however, is doubtful of both assertions. "If you read the art world press, they'll tell you the art world's never going to go into recession because while there isn't money here, there is money in China, India and Russia... But I do think the art market itself is bound to go into some kind of recession and we can expect that there will be a slight downturn in the number of donations and gifts of money to the Tate in the next two or three years." Moreover, he notes, "The Olympics has had a significant effect on the amount of money coming into the Heritage Lottery Fund and into the Arts Council. It's made it much more difficult to fund new projects, particularly in the capital." Serota is less worried about the impact of Hirst's auction, though. "Damien is aware that within the art world, the museums play an important role. So I don't think it'll replace museum shows: we're talking to Damien about doing a show at the Tate."

This is of course good news for fans of Hirst's conceptual art. It will, however, be seen as yet another example of the Tate Director's bias towards conceptual art by his adversaries, in particular the aforementioned Stuckist art group. Serota is having none of it, however: "I'm not alone in this. They bang on about the Tate not doing so, but there are plenty of other museums in this country who could be buying [the Stuckists'] work, but aren't." What's more, he laughs off any suggestion of conceptual partiality: "I don't know where this idea that I don't like figurative painting has emerged from because frankly if you look at the work that we've acquired, I've quite frequently shown artists who work in a figurative fashion... Some of my best friends are figurative painters! But I'd better not be ironic because otherwise you'll print it."